1. Field of the Invention
The present invention relates to a static semiconductor memory device and, more particularly, to a memory device used in environmental conditions where high-energy particle irradiation is such as found in space or in nuclear reactors.
2. Description of the Related Art
Soft errors may occur in a memory device used in severe environments such as space or nuclear reactors where high-energy particle radiation occurs. The circuit construction of a memory cell used in a static random access memory (SRAM) which can enhance the hardness to the soft error caused by irradiation of such high-energy particles is disclosed in IEEE TRANSACTIONS ON NUCLEAR SCIENCE, VOL. 36, DECEMBER 1989, pp. 2318-2322 "SEU CHARACTERIZATION OF HARDENED CMOS SRAMS USING STATISTICAL ANALYSIS OF FEEDBACK DELAY IN MEMORY CELLS" by Ross A, Kohler et al.
However, when the resistance of a feedback resistor R as shown in the above document is increased in order to enhance the hardness to the soft error, the write-in cycle time becomes long, thereby lowering the write-in speed.